Hidden biogeochemical anonymities under Antarctic fast ice

Climate change is negatively affecting the extent of summer sea ice and the global oceanic oxygen concentrations, it is therefore imperative to decipher the life processes under the Antarctic fast ice. The biogeochemical parameters like dissolved oxygen, inorganic carbon, macronutrients, phytoplankton, and chlorophyll a (Chl a) were studied under the fast ice (by drilling ∼1.8 m thick ice) around Larsemann Hills, East Antarctica during India's Scientific Expedition to Antarctica (31-ISEA-2011/12 and 33-ISEA-2013/14). The waters under ice cover were characterized by hyperoxia (up to 10.6 ml/L). Macronutrient concentrations under sea ice were depleted (<0.1 μM NO₃, PO₄ and <2 μM SiO₄); this could be ascribed to the nutrient demand from under ice algae. The water under the ice cover exhibited higher algal biomass (Chl a up to 6.1 mg/m³) and CO₂ under saturation (pCO₂ <10 μatm). This is reflected through the Spearman rank correlation indicating a negative correlation between Chl a and pCO₂ (r=−0.41). The strong negative correlation between dissolved oxygen and pCO₂ (r=−0.67) suggests that photosynthesis regulates the concentrations of both these climatically important gases. The waters under the sea ice cover had brownish mucilaginous aggregates comprised of tube-forming diatoms Berkeleya adelienses and Nitzschia lecointei. These unusual biogeochemical changes were seen only at the ice water interface, and not at deeper depths. This study suggests that with global warming and sea ice melting, Antarctica might witness phytoplankton community shifts.